It is often necessary to route data across a multiplexed network comprising many sources and destinations of many kinds of information. Such information could be a digitized audio conversation between two telephones (termed "duplex" or two-way communications), a data stream from a sensor to a data recorder or computer ("simplex" or one-way transmission), or a transmission from one location to a number of displays (a "multicast"). Several users could be connected together in a conference call setup.
The most common digitization technique is pulse code modulation (PCM). In telephone audio usage this involves taking 8000 samples/second of the analog waveform and quantizing it to 8 bit precision with an analog to digital (A/D) converter. When the bits are serially shifted out, the signal source is called a "DS0", in the North American telecommunications terminology. The "DS0" terminology refers to a well-defined transmission rate and coding scheme in the time-division multiplex hierarchy. The term DS0 generally applies to the 64 Kb component of a DS1 signal that represents the equivalent of a voice channel. Digital signal rates and signal templates are documented by industry standards organizations such as the American National Standards Institute (ANSI), the Conference of European Postal and Telecommunications Administrations, and the CCITT. Examples of the North American digital hierarchy include DS1 (operating at 1.544 Mb/s per second), DS1 C (3.152 Mb/s), and DS3 (44.736 Mb/s). Four DS1 's can be combined into a DS2; .delta.DS2 's compose a DS3. There are also DS4's and DS5's, used for long-distance trunks often running on optical fiber.
A Digital Cross-Connect System (DCS) is a network element that terminates digital signal systems at a particular bit rate, but allows the direct interchange of component signals at a lower bit rate. A DCS 1/0, for example, terminates DS1 systems and interchanges DS0 bit rate channels. A DCS 1/1 interchanges DS1 bit rate channels. A DCS 3/1 has a DS1 interchange, but also allows a DS3 level interface which is demultiplexed to DS1 for switching. A DCS 3/3 has both a DS3 interface and DS3 cross-connect.
A Digital Access Cross-Connect System (DACS) is an electronic digital cross-connect system manufactured by Lucent Technologies Network Systems that has the capability to rearrange the digital signal components of a particular transmission rate. For example, the DACS IV-2000 System is a DS1 cross-connect, and the DACS III-2000 is a DS3 cross-connect.
A Synchronous Optical Network (SONET) is a set of standards for transmission systems operating over optic fiber. The SONET standard is based on the DS3 signal with added bits for overhead information, etc. The basic building block is the Synchronous Transport Level-1 (STS-1) or the Optical Carrier Level-1 (OC-1) at 51.84 Mb/s. The standard provides for higher bit-rate transmission of STS-n and OC-n, where n=1,3,9,12,18,24,36,48.
The particular layout (or "range") within which the method of the invention will be described is shown in FIG. 1. It will be understood that this particular layout is provided for example only, and the method of the invention is not limited to any specific network layout.
Locations or nodes with electronic cross-connects are called main sites (1), and these sites are interconnected with fiber optic (SONET) multiplexers (2). The distances between these sites may be tens of miles apart and the network may have many more sites than are shown here. The sites are connected by links (8), which might be optical, wired, radio, satellite or microwave, as desired. The overall network can be configured as a ring, as shown by links (8), and possibly by secondary links between high-traffic locations, as shown by diagonal link (9).
Most of these multiplexers (see, for example, SONET (3) (FIG. 2) have connections to smaller sites called "feeder sites" (6) that connect to the DS0 (7) and wideband signals at those sites that need to be interconnected across the range. A multiplexer (3) (FIG. 2) that connects to one or more feeder sites is called a breakout site. Main sites may also function as breakout sites.
FIG. 2 shows a detail of a main site (1) and a breakout site (3), with the interconnections among the various devices. The sites connect to the main network (18) with its amplifier/repeater (19) through SONET OC-48 multiplexers (13a-b).
In each of the sites, one or more feeder sites (11a-c), which communicate with their users via DS0-level signals (12a-c), are connected to SONET OC-3 multiplexers (17a-b) via DS1 signals (10a-c). In the main site (1), the OC-3 (17a) is connected to a DCS 3/1 digital cross-connect (14) which in turn is connected via DS3 lines (15) to a DCS 1/0 cross-connect (16). In the breakout site, the OC-3 multiplexer (17b) connects directly to the OC-48 multiplexer (13b).
In a breakout site (3), the DS1 signals (10b-c) from the feeder sites (11b-c) are "hard wired" to the OC-3 SONET multiplexer (17b), but these multiplexers can change the locations of these DS1 signals within the OC-3 multiplexer electronically.
Similarly, in a main site (1) the digital cross-connects DCS 3/1 (14) and DCS 1/0 (16) can change the location of DS0 (12a) and DS1(10a) signals within the DS3 signals (20) that are connected to the OC-48 multiplexer (13a). The DS1 to be cross-connected does not have to have a DS0 within it. An entire "clear channel" DS1, i.e., no channelization for DS0 circuits, can be cross-connected.